JPH11108308A - Water tube boiler and burner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a lowering of NOx and CO in either of the combustion of a liquid fuel or the combustion of a gas fuel. SOLUTION: A burner 10 is arranged to be switched in use for a liquid fuel and a gas fuel and a plurality of water tubes 5 are arranged in a ring at an area where a gas exists during a combustion reaction from the burner 10 within a combustion chamber 9. The burner 10 is so arranged to be switched in use for the liquid fuel and the gas fuel and a plurality of water tubes 5 are arranged in a rang at an area where the gas exists during the combustion reaction from the burner 10 within the combustion chamber 9 to form a first train 6 of water tubes. A clearance is provided between adjacent water tubes 5 of the first water tube train 6 to allow the passage of the gas during the combustion reaction and an area 13 is provided on the perimeter of the first water tube train 6 to continue the combustion reaction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water tube boiler such as a once-through boiler, a natural circulation type water tube boiler, a forced circulation type water tube boiler, and a burner used for the water tube boiler.

[0002]

2. Description of the Related Art A water tube boiler is a boiler in which a can is constituted by water tubes. As a can body structure of such a water pipe boiler, there is a water pipe boiler in which a plurality of water pipes are annularly arranged. In a water pipe boiler of this type, a cylindrical space surrounded by an annular water pipe row is used as a combustion chamber. The water tube boiler as described above,
Heat transfer is mainly performed by radiation in the combustion chamber, and heat transfer is mainly performed by convection downstream of the combustion chamber.

In recent years, there has been a demand for such water tube boilers to further reduce NOx and CO.
Regarding the reduction of NOx, at present, low NO
x It is dealt with by installing a burner or by installing an exhaust gas recirculation device, and coping with low CO by adjusting the combustion state of the burner.

[0004]

An object of the present invention is to achieve low NOx and low CO in both liquid fuel combustion and gaseous fuel combustion.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems. First, in order to achieve low NOx, a burner is provided which switches between liquid fuel and gaseous fuel. A water pipe boiler, wherein a plurality of water pipes are annularly arranged in a region where a gas under combustion reaction from the burner is present in the combustion chamber.

Next, in order to simultaneously reduce the amount of NOx and the amount of CO, a burner for switching between a liquid fuel and a gaseous fuel is provided, and a region in which a gas under combustion reaction from the burner exists in the combustion chamber. A plurality of water pipes are annularly arranged to form a first water pipe row, and a gap is provided between adjacent water pipes of the first water pipe row to allow the flow of gas during combustion reaction,
A water tube boiler, wherein a region for continuously performing a combustion reaction is provided around the first water tube row.

In the above-mentioned water tube boiler, the burner is a diffusion combustion burner.

Further, the present invention relates to a burner for switching between a liquid fuel and a gaseous fuel, comprising a gaseous fuel supply pipe having a flow passage having a substantially annular cross section centering on a nozzle pipe for the liquid fuel, and a cylindrical shape. An air register is arranged coaxially, forming a first air flow path between the nozzle pipe and the gas fuel supply pipe, and forming a second air flow path between the gas fuel supply pipe and the air register. Forming a first baffle plate at the tip of the first air flow path, providing a second baffle plate at the tip of the second air flow path, and forming a tapered portion at the tip of the air register. Burner.
And the second baffle plate is arranged in the middle of the tapered portion, and at the tip of the gaseous fuel supply pipe, an outer jet port for jetting out gaseous fuel outward, and inwardly. A burner provided with an inner ejection port for ejecting gaseous fuel.

Further, the present invention is characterized in that the burner is used for a burner of the above-mentioned water tube boiler.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is embodied as a multi-tube water tube boiler and a burner used in the water tube boiler. Further, the water tube boiler of the present invention is applied as a heat medium boiler for heating a heat medium, in addition to a steam boiler and a hot water boiler.

First, the invention for realizing low NOx reduction will be described. The invention according to claim 1 is provided with a burner that switches between liquid fuel and gaseous fuel and uses a combustion reaction from the burner in a combustion chamber. A plurality of water tubes are annularly arranged in a region where the middle gas exists (hereinafter, referred to as a "combustion reaction region"). The combustion chamber is a space in which a part or all of the inside of the combustion chamber performs a combustion reaction, and may be divided by a water tube row or by an outer wall formed of a refractory or the like. The combustion reaction gas is a high-temperature gas during the combustion reaction in the combustion chamber. The combustion reaction region is preferably a region in which a flame is generated in the combustion reaction gas or a region in which a high temperature of the combustion reaction gas is 900 ° C. or higher. The flame as referred to herein is a phenomenon that occurs in a gas during a combustion reaction in which a combustion reaction is actively performed. This flame may be visible, may be difficult to view, or may not be visible.

Therefore, in the first aspect of the present invention, by arranging a plurality of water pipes in the combustion reaction region, the combustion reaction gas is cooled by the plurality of water pipes to lower the temperature, thereby reducing the temperature of the thermal NOx. Suppress generation.
The reason for this is that, as explained by the Zeldovich mechanism, the higher the temperature of the combustion reaction, the higher the rate of generation of the thermal NOx and the higher the production rate, but the higher the temperature of the combustion reaction, the lower the temperature of the combustion reaction. This is because the generation rate decreases and the generation amount decreases. In particular, when the temperature of the combustion reaction is 1400 ° C. or lower, the generation rate of thermal NOx becomes extremely slow. According to the first aspect of the present invention, since a plurality of water pipes are arranged in a ring,
Since the gas during combustion reaction contacts each water pipe and performs heat transfer,
Since the heat load can be made substantially uniform, and the gas during the combustion reaction is cooled by each water pipe, the reduction of NOx is performed almost uniformly over the entire circumference of the annular water pipe row.

In the first aspect of the present invention, the plurality of water pipes are arranged in a ring shape. As the annular arrangement, the plurality of water pipes are arranged in a perfect circle and also in an elliptical shape. Can also. The plurality of water tubes may be arranged in a triangular shape, a quadrangular shape, or a polygonal shape more than that. Further, when arranging the plurality of water pipes in a ring,
The lines connecting the centers of the water tubes may be arranged so as to form irregularities.

A gap is provided between the adjacent water pipes to allow the gas during the combustion reaction to flow. The gap has such a width that the combustion reaction gas passing through the gap can continue the combustion reaction even when cooled by the water pipes, and the width needs to be at least 1 mm.

[0015] Then, a heat recovery water pipe is arranged outside the water pipe arranged annularly. The heat recovery water pipes further recover heat from the gas during the combustion reaction and the gas after the combustion reaction (hereinafter referred to as “combustion reaction end gas”) that has passed through the gap between the water pipes, thereby improving the efficiency of the water pipe boiler. Let it.

Next, the invention for simultaneously realizing low NOx and low CO will be described. The invention according to claim 2 is provided with a burner for switching between a liquid fuel and a gaseous fuel for use in a combustion chamber. A plurality of water pipes are annularly arranged in a region where the gas during combustion reaction from the burner is present (hereinafter, referred to as “combustion reaction region” as described above) to form a first water pipe row, and a first water pipe row is formed next to the first water pipe row. A gap is provided between the fitted water pipes to allow the gas during the combustion reaction to flow. The meanings of the combustion chamber, the gas under combustion reaction and the combustion reaction zone here are the same as those described in the first aspect, and the same applies to the flame.

In the second aspect of the present invention,
By arranging a plurality of water tubes in the combustion reaction area,
The combustion reaction gas is cooled by the plurality of water pipes to lower the temperature, thereby suppressing the generation of thermal NOx. At this time, the gas during combustion reaction flows through the gaps between the water pipes, so that it comes into contact with more surfaces of the water pipes, so that the above-described effect of reducing NOx by cooling is improved. The reason for this is that, as described in the first aspect, Zeldovich (Zeldov)
ich) As described in the mechanism. According to the second aspect of the present invention, a region where the combustion reaction is continuously performed (hereinafter, referred to as a “combustion reaction continuation region”) is provided around the first water pipe row. The combustion reaction continuation region is a region in which, after the combustion reaction inside the first water pipe row, a combustion reaction of an intermediate product of the combustion reaction such as CO or HC or an unburned portion of the fuel is performed. The gas during combustion reaction flows into the combustion reaction continuation region from the gap, and in the process of flowing through the combustion reaction continuation region, C remaining in the gas during combustion reaction remains.
Since O is oxidized to CO ₂ , the amount of CO discharged from the water tube boiler is reduced. According to the second aspect of the present invention, since a plurality of water pipes are arranged in a ring,
Since the gas during combustion reaction contacts each water pipe and performs heat transfer,
The heat load can be made substantially uniform, and the gas during combustion reaction is cooled by each water pipe, so that the NOx reduction action is performed almost uniformly over the entire circumference of the first water pipe row. Here, as the annular arrangement of the plurality of water pipes, as described in the first aspect, an arrangement of a perfect circle, an ellipse, a polygon, or the like is possible, and the line connecting the centers of the water pipes is uneven. May also be arranged.

Further, in the invention according to claim 2, a gap is provided between adjacent water pipes to allow the flow of the gas during combustion reaction, and this gap is formed by the gas during combustion reaction passing through this gap. It has such a width that the combustion reaction can be continued even when cooled by each of the water pipes. This width should be at least 1
mm is required. The gap does not need to be formed for each adjacent water pipe. For example, a predetermined number of water pipes may be arranged in close contact with each other, and a gap may be provided between groups of the closely connected water pipes. Further, it is not necessary that all of the gaps have the same width, and a plurality of water pipes can be arranged in a ring shape so as to form a wide gap and a narrow gap.

Then, a plurality of heat recovery water pipes are arranged outside the first water pipe row, and the heat recovery water pipes are arranged in a ring to form a second water pipe row. In the combustion reaction continuation region located outside the first water pipe row, the combustion reaction gas is CO 2
In addition to the oxidation reaction, the reaction of the intermediate products of the combustion reaction and the reaction of unburned fuel continue to generate heat. Therefore, by means of each heat recovery water pipe, including these heats,
Heat is recovered from the combustion reaction gas and the combustion reaction end gas. Therefore, the heat can be effectively used by the heat recovery water pipes, and the heat efficiency is further improved. Further, by forming the second water pipe row in an annular shape, each of the heat recovery water pipes comes into almost uniform contact with the combustion reaction gas and the combustion reaction end gas, and performs heat recovery from those gases almost uniformly. Can be.

In the above-mentioned water pipe boiler, the plurality of water pipes are arranged in the combustion chamber such that the temperature of the gas during the combustion reaction after contacting each of the water pipes is 1400 ° C. or less. With this arrangement, the temperature of the gas during the combustion reaction is reduced, and the generation of thermal NOx is reduced, so that the NOx of the boiler can be reduced.

According to a third aspect of the present invention, a diffusion combustion burner is used as the burner. Diffusion combustion is performed in the space inside the annularly arranged water pipe, and good combustion is maintained. In particular, the effect is remarkable in the combustion of liquid fuel.

A fourth aspect of the present invention relates to a burner, and this burner is a diffusion combustion burner that switches between a liquid fuel and a gas fuel. This burner is
A gas fuel supply pipe having a substantially annular cross-section flow path and a cylindrical air register are arranged coaxially around a liquid fuel nozzle pipe. A first air flow path is formed between the nozzle pipe and the gaseous fuel supply pipe, and primary air flows through the first air flow path. A second air flow path is formed between the gaseous fuel supply pipe and the air register, and secondary air flows through the second air flow path. A first baffle plate is provided at a tip of the first air flow path, and a second baffle plate is provided at a tip of the second air flow path, and flame is held by these baffle plates. Forming a tapered portion at the tip of the air register,
The secondary air flow is directed toward the center of the burner. This promotes mixing of the secondary air and fuel,
Low CO can be realized.

According to a fifth aspect of the present invention, the second baffle plate is disposed in the middle of the tapered portion. As a result, the distance between the second baffle plate and the tip of the burner is made as short as possible, the residence time of the combustion gas at the downstream position of the second baffle plate is shortened, and the gas temperature rises due to radiant heat from the flame. Is prevented from doing so. Along with this, it is possible to prevent the flame temperature from rising, thereby realizing a low NOx reduction.

According to a sixth aspect of the present invention, the outer end of the gaseous fuel supply pipe is provided with an outer jet for jetting out gaseous fuel and an inner jet for jetting out gaseous fuel inward. It is. The gaseous fuel jetted from the inner jet port mixes with the primary air to form a small flame downstream of the first baffle plate. This small flame acts as a pilot flame, and the stability of the flame is improved.

According to a seventh aspect of the present invention, the above-described burner is applied as the burner according to the first or second aspect. In both the combustion of liquid fuel and the combustion of gaseous fuel, the combination of the boiler structure for realizing low NOx and low CO and the burner can further achieve low NOx and low CO. .

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a multi-tube once-through boiler will be described below with reference to FIGS. FIG. 1 is an explanatory view of a longitudinal section of an embodiment of the present invention,
FIG. 2 is an explanatory diagram of a cross section taken along line II-II of FIG.

1 and 2, the boiler can 1
Has an upper header 2 and a lower header 3 arranged at a predetermined distance from each other. An outer wall 4 is arranged between the outer circumferences of the upper header 2 and the lower header 3.

Between the upper header 2 and the lower header 3, a plurality (ten in this embodiment) of water tubes 5 are arranged in a ring. These water pipes 5 constitute an annular first water pipe row 6. And, between the upper header 2 and the lower header 3, near the inner peripheral side of the outer wall 4,
A plurality of (30 in the first embodiment) heat recovery water pipes 7 are arranged in an annular shape to form an annular second water pipe row 8. The second water pipe row 8 and the first water pipe row 6 form a double annular water pipe row. Further, each end of each of the water pipes 5 and each of the heat recovery water pipes 7 is connected to each of the upper header 2 and the lower header 3.

The combustion chamber 9 of the boiler is defined by the upper header 2 and the lower header 3 and the second water line 8. A burner 10 is mounted above the combustion chamber 9. The burner 10 is inserted from the inside (central portion) of the upper header 2 toward the combustion chamber 9, and the axis 11 of the burner 10 and each of the water pipes 5 of the first water pipe row 6 are substantially aligned. Being parallel. This burner 10
Is a burner which selectively uses liquid fuel and gas fuel. A liquid fuel supply line 18 and a gas fuel supply line 19 are connected to the burner 10. The liquid fuel supply line 1 serves as a fuel switching means.
8 is provided with a liquid fuel 20 and the gaseous fuel supply line 19 is provided with a gaseous fuel valve 21.

The burner 10 forms a region in the combustion chamber 9 in which a gas under combustion reaction is present, that is, a combustion reaction region. Of the combustion reaction region, a region in which a flame exists (hereinafter referred to as a combustion reaction region). , Called the “flame presence area”
The first row of water pipes 6 is located at the first position. Further, the first water pipe row 6 is arranged in the combustion reaction region such that the temperature of the gas during the combustion reaction after contacting each of the water pipes 5 is 1400 ° C. or less. Further, in the first water pipe row 6, a gap 12 is formed between each of the water pipes 5 so as to allow the gas during the combustion reaction to flow.

Then, between the first water pipe row 6 and the second water pipe row 8, a combustion reaction such as an intermediate product of a combustion reaction such as CO or HC and an unburned portion of the fuel is continuously carried out. (Hereinafter, referred to as a “combustion reaction continuation region”) 13. In the combustion reaction continuation area 13, the water pipe 5
There is no member that absorbs heat as described above.

In the second water pipe row 8, a gap (hereinafter referred to as a "second gap") 14 between adjacent heat recovery water pipes 7 is narrow, and is usually set to 1 to 4 mm. Further, a heat transfer fin 15 is attached to each heat recovery water pipe 7 on the outer peripheral side of the second water pipe row 8.

Further, the outer wall 4 has an exhaust gas outlet 16
Is provided. The exhaust gas outlet 16 communicates with an annular exhaust gas passage 17 between the outer wall 4 and the second water pipe row 8.

In the once-through boiler having the above configuration, when the burner 10 is operated, a gas during combustion reaction is generated in the combustion chamber 9. In the initial stage of the combustion reaction of the gas during the combustion reaction, the fuel is decomposed, and thereafter the decomposed fuel and oxygen react actively. And in the next stage,
Intermediate products such as CO and HC generated in the combustion reaction at this time react further, and the combustion reaction end gas after the combustion reaction is discharged from the can 1 as exhaust gas. Usually, a flame is generated in a region where the combustion reaction is actively performed.

The combustion reaction gas flows in the central portion of the first water pipe line 6 while spreading substantially in the axial direction toward the lower header 3 side, and flows from the gap 12 to the combustion reaction continuation area. 13 flows. Therefore, the flame is
As shown in FIG. 1, the gas is formed to the outside of the first water pipe row 6 with the flow of the gas during the combustion reaction. Therefore, each of the water pipes 5 is located in the flame existing area in the combustion reaction area. Then, the combustion reacting gas which has generated the flame exchanges heat with the fluid to be heated in each of the water pipes 5 when passing through the gaps 12. The combustion reaction gas generating the flame is rapidly cooled by this heat exchange and its temperature is reduced, so that the generation of thermal NOx is suppressed. Here, since the first water pipe row 6 is an annular water pipe row, the combustion reaction gas generating a flame comes into contact with each of the water pipes 5 almost uniformly, so that the heat load on each of the water pipes 5 is reduced. Is also substantially uniform. Further, since the gas during the combustion reaction is substantially uniformly contacted with each of the water pipes 5 and cooled, the action of reducing the NOx by each of the water pipes 5 becomes almost equal. As a result, the formation of a flame is reduced in the combustion reaction gas.

The gas during the combustion reaction that has passed through the gap 12 flows through the combustion reaction continuation region 13 toward the second water pipe row 8. At this time, the gas during combustion reaction does not come into contact with a member that performs heat exchange such as each of the water pipes 5 until the gas reaches the second water pipe row 8, and the temperature does not decrease so much. Therefore, the gas during the combustion reaction flows through the combustion reaction continuation region 13 while continuing the combustion reaction, during which the oxidation reaction from CO to CO ₂ is promoted. In the combustion reaction continuation region 13, in addition to the oxidation reaction, an oxidation reaction of the intermediate product and unburned fuel is performed.

The combustion reaction gas becomes a high-temperature gas that has almost completed the combustion reaction before reaching the second water pipe row 8, and passes through the second gap 14 to the exhaust gas passage 1.
Flow into 7. This combustion reaction gas is supplied to the second gap 14.
, More heat is transferred to the fluid to be heated in each of the heat recovery water pipes 7 by the heat transfer fins 15. The combustion reaction end gas that has passed through the second gap 14 and has flowed into the exhaust gas passage 17 transfers heat from the outside of the second water pipe row 8 to the fluid to be heated in each of the heat recovery water pipes 7. After performing, the exhaust gas is discharged from the boiler through the exhaust gas outlet 16 as exhaust gas. Here, the second water pipe row 8
Because it is an annular water tube row composed of a plurality of heat recovery water tubes 7,
The combustion reaction gas and the combustion reaction end gas almost uniformly contact the heat recovery water pipes 7, and the entire second water pipe row 8 recovers heat from the combustion reaction gas and the combustion reaction end gas. Therefore, also in the second water pipe row 8, the heat load in each of the heat recovery water pipes 7 becomes substantially uniform.

In the above description, the flow of the gas during the combustion reaction is in the radial direction of the first water pipe row 6. Next, the axial direction of the first water pipe row 6 will be described. As described above, the gas during combustion reaction flows through the central portion of the first water pipe row 6 while spreading in the direction of the lower header 3 substantially in the axial direction. The temperature becomes lower toward the downstream side due to the heat transfer to each of the water pipes 5. Therefore, thermal NO
The generation of x is suppressed. Further, since the first embodiment is a once-through boiler, the fluid to be heated is supplied from the lower header 3 into each of the water pipes 5 and each of the heat recovery water pipes 7,
The water pipes 5 and the heat recovery water pipes 7 rise while being heated, and are taken out of the upper header 2 as steam.

Next, the water tube boiler of this embodiment will be described more specifically. This embodiment is implemented as a once-through boiler having an evaporation amount of 500 to 4000 kg per hour. In the once-through boiler of this embodiment, the outer diameter B of the water pipe 5 is about 60 mm. Usually, in a once-through boiler, 25 to 8
Although a water pipe 5 having an outer diameter B of about 0 mm is used, a water pipe 5 having an outer diameter B of about 20 to 100 mm is generally used for a water pipe boiler in general. In this embodiment, as described above, the diameter D of the pitch circle when the plurality of water tubes 5 are arranged in a perfect circle is set to about 344 mm. This diameter D must be at least 100 mm. That is, if the diameter D is smaller than this, the space on the inner peripheral side of the first water pipe row 6 becomes smaller, and it becomes difficult to continue a stable combustion reaction. On the other hand, when the diameter D is large, the space on the inner peripheral side of the first water pipe row 6 becomes large, and a high-temperature region which promotes the generation of thermal NOx is easily generated therein. Therefore, the upper limit of the diameter D is determined in consideration of this point. The upper limit of the diameter D is determined according to the required amount of evaporation of the boiler. For example, in a water tube boiler having an evaporation amount of 4000 kg per hour, the upper limit of the diameter D is 1000 mm.

In this embodiment, the distance A between the centers of the adjacent water pipes 5 in the first water pipe row 6 is set to about 106 mm, and the ratio A / B of the distance A between the centers and the outer diameter B of the water pipes 5 is set.
Is set to 1.8. When the gap 12 is provided between the water pipes 5 as in this embodiment, the width C of the gap 12
Is set to a value such that the combustion reaction gas does not stop the combustion reaction due to cooling by the water pipes 5. In this case, the width C of the gap 12 needs to be at least 1 mm. Therefore, when the gap 12 is provided between the adjacent water pipes 5, the ratio A / B is set to 1 <A / B ≦ 2. This ratio A /
B can be changed according to the degree of the demand for NOx reduction. At this point, the width C of the gap 12 in the embodiment is equal to the difference between the center-to-center distance A and the outer diameter B, and is about 46 mm.

Further, the burner 10 in this embodiment is
Sets the air ratio to 1.3, in which case
The maximum temperature of the gas during the combustion reaction is approximately 1700 ° C.
Here, in a burner for a water tube boiler, combustion is generally performed with the air ratio set in the range of 1.1 to 1.3. In this case, the maximum temperature of the gas during the combustion reaction is set at 1.1 when the air ratio is 1.1. ~
It is approximately 1800 ° C. in the range of 1.2, and the air ratio is 1.2
Approximately 1700 ° C. in the range of 1.3.

As described above, by setting the distance A between the centers of the water pipes 5 and the outer diameter B, the temperature of the gas during the combustion reaction at the time of passing through the gap 12 can be reduced by the cooling by the water pipes 5. To about 1100 ° C. This temperature is equal to or lower than the temperature (approximately 1400 ° C.) at which the amount of generated thermal NOx is greatly reduced. Therefore, it is possible to provide a once-through boiler that emits a small amount of NOx. Incidentally, the NOx emission of the once-through boiler of the first embodiment is O ₂
It is about 30 ppm in terms of 0%. And this temperature is
The temperature is higher than the temperature at which the oxidation reaction from CO to CO ₂ is actively performed (about 800 ° C.). Therefore, when the combustion reaction gas flows through the combustion reaction continuation region 13, CO 2
Oxidation reaction from to CO ₂ will be actively performed,
A once-through boiler that emits less CO can be provided.

As described above, in the once-through boiler of this embodiment, the temperature of the combustion reaction gas flowing out of the gap 12 of the first water pipe row 6 is controlled to approximately 1100 ° C. 8 according to the degree of low CO demand
Control is performed within the range of 00 to 1400 ° C. Here, the temperature of the combustion reaction gas flowing out of the gap 12 is low NOx.
It is preferably as low as possible from the viewpoint of reducing CO, and more preferably as high as possible from the viewpoint of reducing CO. In this regard, the temperature is more preferably in the range of 900 to 1300 ° C.

In this embodiment, the radial interval E between the first water pipe row 6 and the second water pipe row 8 is set as the width of the combustion reaction continuation area 13. The interval E
Is about 84 mm, which is 1.4 times the outer diameter B. In this way, by setting the interval E, the residence time of the gas during the combustion reaction in the combustion reaction continuation region 13 is adjusted to about 47 milliseconds. In this case, C
The amount of O emission is about 15 ppm. That is, in order to ensure that the oxidation reaction occurs, the temperature of the gas during the combustion reaction is maintained at a certain temperature (about 800 ° C.) or higher,
A certain reaction time is required. This reaction time is required to be shorter as the temperature of the gas during the combustion reaction is higher, and to be longer as the temperature is lower. Therefore, the set value of the interval E is changed according to the temperature of the combustion reaction gas flowing out from the gap 12,
The residence time of the gas during the combustion reaction in the combustion reaction continuation region 13 is adjusted. Also, the number and width C of the gap 12
, The interval E is changed. The lower limit of the residence time is selected from the range of 1 to 10 milliseconds. Therefore, the lower limit of the interval E is about 0.5 times the outer diameter B.
Further, it is advantageous to set the residence time to be relatively long in terms of reducing CO, but it is determined according to the degree of demand for lowering CO and miniaturizing the boiler. In this case, the upper limit of the interval E is preferably about six times the outer diameter B.

Next, an embodiment of a burner according to the present invention will be described with reference to FIGS. FIG.
FIG. 4 is an explanatory view of a vertical section of an embodiment of a burner according to the present invention, and FIG. 4 is an explanatory view of a bottom surface of FIG.

The burner 10 is provided with a nozzle pipe 22 for liquid fuel at the center thereof, and a gas fuel supply pipe 23 having a flow passage having a substantially annular cross section and a cylindrical air register 24 formed coaxially around the nozzle pipe 22. Has been placed. A first air flow path 25 through which primary air flows is formed between the nozzle pipe 22 and the gas fuel supply pipe 23, and secondary air flows between the gas fuel supply pipe 23 and the air register 24. A second air flow path 26 is formed. These combustion air are supplied by a blower (not shown). The ratio of primary air to secondary air is 10 to 2
0%, and the secondary air is set at 90-80%. Liquid fuel and gaseous fuel are alternately supplied.

At the end of the nozzle pipe 22, two nozzle tips 27 for spraying liquid fuel are provided. The liquid fuel is sprayed from both nozzle tips 27 during high combustion, and the liquid fuel is sprayed from one nozzle tip 27 during low combustion. The first baffle plate 2 is located at the tip of the first air flow path 25, that is, at a position downstream of the nozzle tip 27.
8 are provided. The first baffle plate 28 has an opening 34 at the center and six turning blades 35 around the opening 34. A second baffle plate 29 is provided at the tip of the second air flow path 26. The second baffle plate 29 has six notches 30 substantially uniformly in the circumferential direction on the outer peripheral portion thereof.
Is provided. The secondary air circulates through the notch 30 (the flow velocity is 30 to 50 m / s). By dividing the secondary air by the cutout portion 30 and supplying the divided fuel to the fuel, a divided flame is formed, so that the NOx reduction can be realized.

The tip of the air register 24 has a tapered portion 3
1 is formed, and the tip of the air register 24 is tapered. The taper angle is set to about 20 degrees. With this structure, the flow of the secondary air becomes a flow toward the center of the burner 10, and the mixing of the secondary air and the fuel is promoted, so that low CO can be realized.

The second baffle plate 29 is disposed in the middle of the tapered portion 31. By doing so, the secondary air after obtaining the flow in the center direction of the burner by the tapered portion 31 is divided, and the secondary air is divided without impairing the flow of the secondary air in the center direction. be able to. Further, the distance between the second baffle plate 29 and the tip of the burner 10 is shortened as much as possible, so that the residence time of the combustion gas at the downstream position of the second baffle plate 29 is shortened. Is prevented from rising. Along with this, it is possible to prevent the flame temperature from rising, thereby realizing a low NOx reduction.

At the distal end of the gaseous fuel supply pipe 23, an outer jet 32 for jetting gaseous fuel outward and an inner jet 33 for jetting gaseous fuel inward are provided. A plurality of these outer jet ports 32 and inner jet ports 33 are provided in the circumferential direction, and the opening area of the outer jet port 32 is larger than the opening area of the inner jet port 33. Since the outer jet port 32 is provided at a position downstream of the second baffle plate 29, it is not necessary to supply gaseous fuel at a high pressure,
Supply at low pressure is possible. The gaseous fuel jetted from the inner jet port 33 is mixed with primary air,
A small flame is formed downstream of the first baffle plate 28. This small flame acts as a pilot flame, and the stability of the flame is improved.

The operation of the burner 10 will be described. At the time of supplying the liquid fuel, the liquid fuel is sprayed from the tip of the nozzle tip 27, firstly mixed with the primary air from the first air passage 25, and then the secondary air from the second air passage 26 And a flame is formed at a position downstream of the first baffle plate 28. The secondary air is divided and supplied by the second baffle plate to form a divided flame, so that a low NOx can be achieved. Further, the action of the tapered portion 31 of the air register 24 promotes the mixing of the secondary air and the liquid fuel, thereby achieving a low CO.

On the other hand, at the time of supplying gaseous fuel, gaseous fuel is jetted from the outer jet port 32 and the inner jet port 33, and the gas fuel jetted from the inner jet port 33 is
When mixed with the primary air from the first air passage 25, a small flame is formed at a position downstream of the first baffle plate 28. This small flame acts as a pilot flame, and the flame holding property is improved. The gaseous fuel jetted from the outer jet port 32 mixes with the secondary air from the second air flow path 26 to form a large flame downstream of the second baffle plate 29. The secondary air is divided and supplied by the second baffle plate to form a divided flame, so that a low NOx can be achieved. Further, by the action of the tapered portion 31 of the air register 24, mixing of the secondary air and the gaseous fuel is promoted, and the low C
O conversion can be achieved.

The burner 10 is employed as a burner of the above-mentioned once-through boiler, and the both effects of low NOx and low CO can further reduce NOx and CO. Further, since the burner 10 is used by selectively switching between liquid fuel and gaseous fuel, even if supply of any fuel becomes impossible due to a change in fuel supply,
The operation can be continued by switching to another fuel. For example, even if the supply network of the gaseous fuel is cut off due to a disaster or accident, the operation can be continued by using the liquid fuel.

[0054]

As described above, according to the present invention, in both the combustion of liquid fuel and the combustion of gaseous fuel,
It is possible to further reduce NOx and to reduce NO.
It is possible to provide a water pipe boiler and a burner with clean exhaust gas that can achieve x reduction and low CO at the same time and that respond to environmental issues.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a vertical section of an embodiment of a water tube boiler according to the present invention.

FIG. 2 is an explanatory view of a cross section taken along line II-II of FIG.

FIG. 3 is an explanatory view of a longitudinal section of an embodiment of a burner according to the present invention.

FIG. 4 is an explanatory diagram of a bottom surface in FIG. 3;

[Explanation of symbols]

 Reference Signs List 1 can body 2 upper header 3 lower header 4 outer wall 5 water pipe 6 first water pipe row 7 heat recovery water pipe 8 second water pipe row 9 combustion chamber 10 burner 11 axis 12 gap 13 combustion reaction continuation area 14 second gap 22 nozzle pipe Reference Signs List 23 gas fuel supply pipe 24 air register 25 first air flow path 26 second air flow path 27 nozzle tip 28 first baffle plate 29 second baffle plate 30 cutout portion 31 taper portion 32 outer jet port 33 inner jet port A adjacent Distance between centers of matching water pipes B Outside diameter of water pipe C Width of gap E Width of combustion reaction continuation area

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI F23D 17/00 101 F23D 17/00 101

Claims (7)

[Claims] A burner for switching between a liquid fuel and a gaseous fuel; and a plurality of water pipes arranged annularly in a combustion chamber in a region where a gas under combustion reaction from the burner exists. Water tube boiler. 2. A burner 10 for switching between a liquid fuel and a gaseous fuel is used, and a plurality of water pipes 5 are annularly arranged in a region where a gas under combustion reaction from the burner 10 is present in a combustion chamber 9. A first water pipe row 6 is formed, a gap 12 is provided between adjacent water pipes 5 of the first water pipe row 6 to allow the flow of gas during combustion reaction, and a combustion reaction is continued around the first water pipe row 6. A water tube boiler, wherein a region 13 is provided. 3. The water tube boiler according to claim 1, wherein the burner is a diffusion combustion burner. 4. A burner for switching between a liquid fuel and a gaseous fuel, the gaseous fuel supply pipe having a flow passage having a substantially annular cross section around a nozzle pipe 22 for the liquid fuel.
And a cylindrical air register 24 disposed coaxially, a first air flow path 25 is formed between the nozzle pipe 22 and the gas fuel supply pipe 23, and the gas fuel supply pipe 23 and the air register 24 are formed. A second air flow path 26 is formed between the first air flow path 25 and a first baffle plate 28
A second baffle plate 29 is provided at the tip of the second air passage 26, and a tapered portion 3 is provided at the tip of the air register 24.
Burner characterized by forming No. 1. 5. The burner according to claim 4, wherein the second baffle plate is disposed in the middle of the tapered portion. 6. An outer outlet 32 for ejecting gaseous fuel outward and an inner outlet 33 for ejecting gaseous fuel inward at a distal end of the gaseous fuel supply pipe 23. The burner according to claim 4. 7. A water pipe boiler, wherein the burner according to claim 1 or 2 is the burner according to claim 4.